High strength aluminum alloy for pellet extrusion and product



United States Patent 3,177,073 HIGH STRENGTH ALUMINUM ALLOY FQR PELLET EXTRUSIUN AND PRODUCT George S. Foerster, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Mar. 26, 1962, Ser. No. 132,648. 2 Claims. (Cl. '75-i47) This invention relates to aluminum alloys and more particularly is concerned with a novel aluminum alloy having particular utility in the preparation of high strength pellet extrusions, to the extruded product and to the process for preparing the product.

In general, this novel aluminum base alloy contains on a Weight basis from about 0.5 to about 2.0 percent magnesium, from about 0.5 to about per-cent silicon, from about 0.5 to about '10 percent of an additive metal, balance aluminum, wherein the silicon and additive metal are maintained within a predetermined ratio and the silicon content is at least equal to or in excess of that needed for formation of magnesium :silicide (Mg Si).

Iron and chromium are employed as the additive metals in this alloy. Chromium is especially preferred as additive since this does not lower the excellent corrosion resistance generally inherent in aluminum base alloys containing magnesium and silicon. The actual amount of additive to be employed in the alloy is varied in accordance with the properties and, characteristics, eg. density, etc., desired in the extruded product. The actual silicon content employed in the alloy, within the range of from 0.5 to 10 percent as set forth hereinbefore, is established in accordance with the equation:

Wt. percent Si fi -i-K (weight percent additive member) Minimum K values vto be used with the additives to assure the incorporation of the desired amount of silicon into the alloy are 0.5 for chromium and 0.2 for iron. Preferably for optimum alloy properties the minimum silicon content is determined using the following K values in the equation; chromium (1.1) and iron (0.5).

Theoperable concentration range and preferred concentration range of these same additive metals in the alloy are shown in Table I.

The additive members can be used alone in the alloy or a mixture of additives can be employed. With mixtures of additive metals, the concentration of each of the individual members used therein is proportionally reduced so that the total concentration of the additive in the alloy falls within the range and in accordance with the relationship set forth hereinbefore.

The alloy is prepared using foundry alloying and melt techniques as practiced in the aluminum art.

This alloy particularly is suitable for fabricating high strength pellet extrusions. the alloy is prepared and rapidly solidified as by atomizing into pellets. Conveniently the pellets can be produced In this operation, a melt of ice by jet atomizing or wheel atomizing either in an inert atmosphere such as natural gas, nitrogen, argon, etc. for example, or in air. The atomized pellets are fabricated into high strength extrusions using normal pellet extrusion techniques and apparatus.

In this process, because of the rapid cooling of the small pellets the dispersed second phase is present inthe alloy in much finer form than in a massive ingot which has a relatively slow cooling rate. Therefore, high strength fabrications exhibiting satisfactory elongation, i.e. ductility in the final product can be extruded using these alloys having the metal ratios and concentrations set forth here- For use in the pellet extrusion process, ordinarily the pellets are preheated to a temperature at least that of the extruder container and the heated pellets then are loaded into the containerv and extruded. However, if desired, the pellets can be used in the extrusion process without preheating. Also the pellets can be precompacted prior to extrusion. By precompacting the pellets under reduced pressure, blistering and formation of internal voids substantially are avoided during any post extrusion heat treatment that may be employed.

The so-extruded product can be solution heat treated,

quenched and aged, if desired. In this treatment, prefer ably the length of time for solution heat treatment is minimized to avoid (l) agglomeration of any dispersed phase that might be present in the alloy, (2) recovery, (3) recrystallization and (4) loss of strength.

For those alloys which contain silicon in excess of the solid solubility of this element in the alloy, high strength extrusions and particularly pellet extrusions unexpectedly can be produced at relatively low extrusion temperatures, i.e. from about 750 to about 850 F. Further increase in the strength of the extrusion results by directly quenching the extruded product as it emerges from the die and subsequently aging.

The following example will serve to illustrate further the utility of the present invention but is not meant to limit it thereto.

' Example 1 I An aluminum base-magnesium silic'on alloy containing chromium or iron as an additive member was prepared. The alloy was atomized into pellet form. The pellets had a mesh distribution of about -20 +200 (US. Standard Sieve) the balance passing through the 200 mesh sieve.

A batch of the atomized pellets was preheated to about 700 F. and placed in the pellet container of a ram extruder which container also was about this same temperature.

The pellets were extruded at an extrusion temperature of about 800 F. and an extrusion rate of about 5 feet per minute into a strip 0.2 inch thick by 1 inch wide. The resulting strip then was solution heat treated at about 970 F. for /2 hour, quenched and aged 16 hours at 320 F.

As a control, an alloy containing predetermined amounts of magnesium and silicon without any additive metal was prepared and cast both into ingot and pellet form, extruded and similarly heat treated. A further control was established by adding predetermined quan tities of the additive metals to the magnesium-silicon containing alloy and again extruding similar strips from a 3-inch diameter ingot of the alloy. The control extrusions subsequently were heat treated as described hereinbefore.

Standard test bars were prepared and the percent elongation, tensile yield strength and tensile strength or" the alloys determined at room temperature. The results of these tests are presented in Table II which follows.

TABLE II- Percent by wt. Test Results Extrusion Run No. Other K Form Remarks Mg Si E, percent TYS, 1000 TS, 1000 r 1 p.s.i. p.s.1.

1. 2 0. 7 14 35 40 I+P 1. Control-No additive. 1. 2 0.7 .4 36 40 1-.-- .ControL. 1.0 1.0 13 28 P- 1. 9 2. 4 6 45 52 P Mn/Crratio in inoperative range. 1, 3.5 52 59 P- j 1. 2 0. 7 10 I Control. 1.2 0.8 0.02 12 26 41' 1. 2 .2. 0 0. 2 4 41 60' Mn/Fe ratio in inoperative range. 1.2 4. Q 6 Fe- 0.55 4 55 62 -P I=Ingot, P =Pellet.

hese 1 .3 fileeilysheit he nexpec ed. Pr o increase-in strength obtained from pellet extrusions pre- 1 pared from alloys having a composition in accordance with that set forth he'reinbetore as well as demonstrates the need for maintainingthe additive metal/silicon ratio the: range prescribed herein- Various modifications can be made in the present invention. without departing from thespirit or scope thereof rent is understqod that LI limit myselfonly as defined in the apended elaims.

1 claim 1 1. An aluminumalloy.consistingessentially of from about 0.5 to about 2.0 weight percent magnesium, from about 0.5 12001301112 10 weight percent silicon, an additive r n'etal, balance aluminum, said additive metal'being a member selected from the group consisting of chromium and iron and the concentration inweight percent of said additive metal in said alloy being from about 1.5 to about 3,for chr ornium and from about 3 to about 6 for iron, the

weight percent of silicon in said alloybeing predetermined within'the range of from, about,0.5 toabout 10 percent in accordance with the equation Wt. percent Si= 1 (wt? percent additive metal) where Kis 1.1 for'chrornium' and 0.5v for iron.

.,52;,;A- high: strength aluminum alloy pellet extrusion formed from a pelletized aluminum alloy'consisting essentially of from 0.5 to about "2 weight percent magnesiurn, fr m about-0.5 to about 10 weight percent silicon,anfadditiv1e in'e'tal, andfreniaiiide'r aluminum, said, ad-- ditive metal being a member selected from the group .con-

l 1.1 (1.5 to 3 wt. percent chromium) 0.513%6 .Wt. percent iron) said extrusion beingcharacterized in the erttrudeijs'olu tion heat treated, ,quenchedand aged condition by an unexpectedly high tensile strength. 1

R f rews Cited by eExaaineri UNITED STATES PATENTS, 2,053,925 V 9/36 Stroup -75- 147 2,280,172 4/42 Stroup "75+147 2,454,312 11/48 Fritzlen (vs-147x 2,966,731 1/61 Towneretal. -,138X 3,031, 99; .4/62 Criner "75-448 FOREIGN PATENTS 357,805 10/31 Great Britain.

440,600 1/36 Great Britaiin',

977,514 4/ 5l France,

DAVID'L. RE K, Primary Eramir zer. 7 

1. AN ALUMINUM ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 0.5 TO ABOUT 2.0 WEIGHT PERCENT MAGNESIUM, FROM ABOUT 0.5 TO ABOUT 10 WEIGHT PERCENT SILICON, AN ADDITIVE METAL, BALANCE ALUMINUM, SAID ADDITIVE METAL BEING A MEMBER SELECTED FROM THE GROUP CONSISTING OF CHROMIUM AND IRON AND THE CONCENTRATION IN WEIGHT PERCENT OF SAID ADDITIVE METAL IN SAID ALLOY BEING FROM ABOUT 1.5 TO ABOUT 3 FOR CHROMIUM AND FROM ABOUT 3 TO ABOUT 6 FOR IRON, THE WEIGHT PERCENT OF SILICON IN SAID ALLOY BEING PREDETERMINED WITHIN THE RANGE OF FROM ABOUT 0.5 TO ABOUT 10 PERCENT IN ACCORDANCE WITH THE EQUATION 